The US Open Cup has only had a Fourth Round (prior to the Quarterfinals) 12 times in the Modern Era (2003, 2004, 2005, 2006, 2012-22).
The first indoor game in US Open Cup history took place in the Fourth Round. On July 20, 2004, the Minnesota Thunder hosted the Los Angeles Galaxy at the Hubert H. Humphrey Metrodome in Minneapolis, Minn. The Thunder upset the Galaxy that day 1-0, in front of 5,505 fans. Defender Chris Brunt scored the game-winning goal in the 21st minute.
No Open Division team in the Modern Era has ever advanced beyond the Fourth Round
Only 7 USL League Two (PDL) teams have advanced to the Fourth Round, all but one have faced MLS teams
2018: FC Golden State Force (lost 3-1 at Los Angeles Galaxy)
2016: Kitsap Pumas (lost 2-0 at Seattle Sounders FC)
2014: Laredo Heat (lost 1-0 at Houston Dynamo)
2014: Orlando City U23s (lost 3-0 at Portland Timbers)
2012: Michigan Bucks (lost 2-1 AET vs. Dayton Dutch Lions)
2006: Carolina Dynamo (lost 4-2 vs. Houston Dynamo)
2005: Des Moines Menace (lost 6-1 vs. Kansas City Wizards)
2003: Fresno Fuego (lost 3-1 vs. Los Angeles Galaxy)
Only 6 Open Division Local (USASA) teams have advanced to the Fourth Round
2018: NTX Rayados (lost 5-0 at Houston Dynamo)
2017: Christos FC (lost 4-1 at D.C. United of MLS)
2016: La Maquina (lost 4-1 AET at Los Angeles Galaxy of MLS)
2015: PSA Elite (lost 6-1 at Los Angeles Galaxy of MLS)
2014: PSA Elite (lost 5-0 at Seattle Sounders of MLS)
2012: Cal FC (lost 5-0 at Seattle Sounders of MLS)
2006: Dallas Roma FC (lost 2-0 at Los Angeles Galaxy of MLS)
In 2006, only teams from Major League Soccer emerged from the Fourth Round.
The Chicago Fire did not lose a Fourth Round game until 2019 when they lost to Saint Louis FC. Prior to that, they had a 7-0-2 (2-0 PKs) record.
Major League Soccer began playing in the tournament in the Fourth Round for the first time in 2014 as part of an expanded format.
The attendance record in the Modern Era was set in 2013 when Sporting Kansas City (MLS) hosted Orlando City SC (USL PRO) at Sporting Park in front of an announced attendance of 15,981. Thanks to that figure, the record for Fourth Round average attendance was broken with 6,887 across the eight games. Sporting Kansas City later broke their own record in 2015 when they hosted and defeated Saint Louis FC (USL) 1-0 on June 16, 2015 in front of an announced crowd of 19,298. FC Cincinnati shattered that record in 2017 when they drew 30,160 to Nippert Stadium to watch them upset the Columbus Crew (MLS), 1-0.
In 2014, with Major League Soccer not entering the tournament until Round 4, a record three amateur teams (Laredo Heat, Orlando City U23s, PSA Elite) advanced beyond the Third Round, followed by five amateur teams reaching the Fourth Round in 2015.
Notable upsets in the Fourth Round
2003: Wilmington Hammerheads (PSL) 4:1 Dallas Burn (MLS)
2003: Seattle Sounders (A-League) 1:0 San Jose Earthquakes (MLS)
2004: Charleston Battery (A-League) 1:0 Metrostars (MLS)
2004: Rochester Raging Rhinos (A-League) 1:1 New England Revolution (MLS) (ROC advances on PKs 3-1)
2004: Richmond Kickers (PSL) 2:1 DC United (MLS)
2004: Minnesota Thunder (A-League) 1:0 Los Angeles Galaxy (MLS)
2005: Rochester Raging Rhinos (USL-1) 3:1 Metrostars (MLS)
2005: Minnesota Thunder (USL-1) 4:1 Colorado Rapids (MLS)
2012: Harrisburg City Islanders (USL PROro) 3:1 (AET) New York Red Bulls (MLS)
2012: Charlotte Eagles (USL PRO) 2:1 (AET) San Antonio Scorpions (NASL)
2013: Carolina RailHawks (NASL) 3:1 (AET) Chivas USA (MLS)
2013: Orlando City SC (USL PRO) 1:0 Sporting Kansas City (MLS)
2014: Atlanta Silverbacks (NASL) 2:1 Real Salt Lake (MLS)
2014: Carolina RailHawks (NASL) 1:1 (3:2 PKs) Chivas USA (MLS)
2014: New York Cosmos (NASL) 3:0 New York Red Bulls (MLS)
2014: Rochester Rhinos (USL) 1:0 DC United (MLS)
2015: Charlotte Independence (USL) 1:0 New England Revolution (MLS)
2015: New York Cosmos 2:2 (4:3 PKs) New York City FC (MLS)
2016: New York City FC (MLS) 0:1 New York Cosmos (NASL)
2016: D.C. United (MLS) 0:0 (3:4 PKs) Fort Lauderdale Strikers (NASL)
2017: Columbus Crew (MLS) 0:1 FC Cincinnati (USL)
2017: Miami FC (NASL) 3:1 Orlando City SC (MLS)
2017: Sacramento Republic FC (USL) 4:1 Real Salt Lake (MLS)
2018: Louisville City FC (USL) 3:2 New England Revolution (MLS)
2018: Nashville SC (USL) 2:0 Colorado Rapids (MLS)
2018: Sacramento Republic FC (USL) 2:1 (AET) Seattle Sounders FC (MLS)
2019: Saint Louis FC (USL-C) 2:1 Chicago Fire (MLS)
2019: Colorado Rapids (MLS) 2:2 (2:4 PKs) New Mexico United (USL-C)